manim plugins -l does nto show manim-pptx as a plugin

[krishvk]

Hello @RythenGlyth

I have installed both plugins pip install manim-fontawesome and pip install manim-pptx with pip successfully

> pip list | grep manim

manim                         0.15.2
manim-fontawesome             6.0.0
manim-pptx                    0.1.6

However, manim plugins -l does not show manim-pptx for somereason

> manim plugins -l

Manim Community v0.15.2

Plugins:
 • manim_fontawesome

[RythenGlyth]

I'm not sure if this is a problem. If you know how to add it to the list, a PR would be appreciated.
Does it work though?